The present invention relates to an image-pickup apparatus that performs a scan operation for sequentially obtaining focus evaluation values from video signals with movement of a focus lens and calculates an in-focus position of the focus lens based on the focus evaluation values.
Many image-pickup apparatuses such as digital cameras employ an auto focus (AF) method referred to as a TV-AF method. As shown in FIG. 6, the TV-AF method causes a focus lens to move in a predetermined movable range (for example, a range from an infinite end to a close end) to obtain AF evaluation values from the video signals at respective focus lens positions. The method subsequently determines, as an in-focus position, a focus lens position at which a maximum AF evaluation value is obtained (see Japanese Patent Laid-Open No. 3-68280).
Further, in the TV-AF method, when a focal length of an image-pickup optical system is long and the movable range of the focus lens is wide, or when a depth of field of the image-pickup optical system is small so that the focus lens needs to be finely moved, a great number of samples of the AF evaluation values need to be obtained. In this case, it takes long time to collect the AF evaluation values, resulting in disabling a high-speed AF operation.
Japanese Patent Laid-Open No. 2004-109150 discloses an image-pickup apparatus that divides an entire object distance range (that is, an entire movable range of the focus lens) into plural zones and that selects from the plural zones a zone for actually moving the focus lens to obtain the AF evaluation values. Further, the image-pickup apparatus appropriately changes the zone where the focus lens is moved based on a predetermined condition, thereby realizing a high-speed AF operation.
However, even in the case where the zone for obtaining the AF evaluation values is selected as disclosed in Japanese Patent Laid-Open No. 2004-109150, if the movable range of the focus lens is wide enough to include a macro range and a non-macro range, a large number of zones can be selected. As a result, the number of samples of the AF evaluation values may be extremely large.